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United States Patent |
5,692,409
|
Cheers
,   et al.
|
December 2, 1997
|
Production of metal containers
Abstract
A die for the toolpack of a wall-ironing apparatus for forming metal cans
is laterally displaceable for accommodating misalignment of the
wall-ironing punch from its central axis. Restoring force to return the
die to its own central position is provided by pneumatically operated
biassing elements. For increasing the restoring force available, those
biassing elements which are on the upstream side of lateral die movement
are rendered ineffective on the die by engagement with stops located at
the central die position. Usually, as described, the die is one of a pair
of dies coupled for lateral movement together.
Inventors:
|
Cheers; Christopher Francis (Wantage, GB);
Hill; Brian (Swindon, GB);
Porucznik; Paul (Kennington, GB)
|
Assignee:
|
Carnaudmetalbox (Holdings) USA, Inc. (Wilmington, DE)
|
Appl. No.:
|
517470 |
Filed:
|
August 21, 1995 |
Foreign Application Priority Data
Current U.S. Class: |
72/349; 72/468 |
Intern'l Class: |
B21D 022/00; B21D 022/21; B21C 003/06 |
Field of Search: |
72/468,347,349,465,467,285,379.4
|
References Cited
U.S. Patent Documents
3656335 | Apr., 1972 | Kaminski | 72/467.
|
4262512 | Apr., 1981 | Maeder | 72/349.
|
4554815 | Nov., 1985 | Weishalla | 72/349.
|
4843863 | Jul., 1989 | Grims et al. | 72/349.
|
4926669 | May., 1990 | Grims et al. | 72/349.
|
5016462 | May., 1991 | Grims et al. | 72/349.
|
5235842 | Aug., 1993 | Freeman et al.
| |
Other References
EP Search Report dated Mar. 22, 1995.
Annex to Search Report Oct. 24, 1994.
|
Primary Examiner: Larson; Lowell A.
Assistant Examiner: Butler; Rodney A.
Attorney, Agent or Firm: Diller, Ramik & Wight, PC
Claims
We claim:
1. An apparatus for the production of a metal container comprising an
annular die, a punch movable through the annular die along a punch axis,
said die being movable laterally in relation to the punch axis from a
predetermined central position, biassing means for biassing the die
towards the predetermined central position when the die is laterally
displaced from the predetermined central position and towards the biassing
means, said biassing means including a plurality of spaced biassing
pistons disposed exteriorly around the die at predetermined locations,
fluid pressure means interposed between the die and the biassing pistons
for continuously urging the biassing pistons radially outwardly away from
the die, each biassing piston being located at least in part in a piston
chamber under the influence of said fluid pressure means, each said
biassing piston and piston chamber including respective first and second
stop means which abut each other under the influence of said fluid
pressure means and limit lateral outward movement of said biassing pistons
relative to said piston chambers, and fixed abutment means laterally
outwardly of said first and second stop means against which said biassing
pistons selectively abut and release whereby upon lateral displacement of
said annular die from its predetermined central position at least one
biasing piston wall abut said fixed abutment means during which the
associated first and second stop means will be spaced from each other and
at least one further biassing piston will be spaced from said fixed
abutment means during which its associated first and second stop means
will be in abutment with each other thereby affecting restoration of said
annular die to its punch axis relationship.
2. The apparatus as defined in claim 1 wherein said fluid pressure means
include a bladder for imparting fluid pressure forces to said biassing
pistons.
3. The apparatus as defined in claim 1 wherein said first stop means is a
flange of each biassing piston.
4. The apparatus as defined in claim 1 wherein said second stop means is a
surface of each piston chamber opposing its associated biassing piston
first stop means.
5. The apparatus as defined in claim 1 wherein said first stop means is a
flange of each biassing piston, and said second stop means is a surface of
each piston chamber opposing its associated biassing piston flange.
6. The apparatus as defined in claim 1 including an outer housing member
surrounding said biassing pistons, portions of said biassing pistons
project through openings in said outer housing member, and said fixed
abutment means are located exteriorly of said outer housing member.
7. The apparatus as defined in claim 2 wherein said second stop means is a
surface of each piston chamber opposing its associated biassing piston
first stop means.
8. The apparatus as defined in claim 2 wherein said first stop means is a
flange of each biassing piston, and said second stop means is a surface of
each piston chamber opposing its associated biassing piston flange.
9. The apparatus as defined in claim 2 including an outer housing member
surrounding said biassing pistons, portions of said biassing pistons
project through openings in said outer housing member, and said fixed
abutment means are located exteriorly of said outer housing member.
10. The apparatus as defined in claim 9 wherein said second stop means is a
surface of each piston chamber opposing its associated biassing piston
first stop means.
11. The apparatus as defined in claim 9 wherein said first stop means is a
flange of each biassing piston, and said second stop means is a surface of
each piston chamber opposing its associated biassing piston flange.
12. The apparatus as defined in claim 9 including an outer housing member
surrounding said biassing pistons, portions of said biassing pistons
project through openings in said outer housing member, and said fixed
abutment means are located exteriorly of said outer housing member.
13. An apparatus for the production of a metal container comprising an
annular die, a punch movable through the annular die along a punch axis,
said die being movable laterally in relation to the punch axis from a
predetermined central position, biassing means for biassing the die
towards the predetermined central position when the die is laterally
displaced from the predetermined central position and towards the biassing
means, said biassing means including a plurality of spaced biassing
pistons disposed exteriorly around the die at predetermined locations,
fluid pressure means for continuously urging said biassing pistons
radially inwardly toward and against said die, each biassing piston being
located at least in part in a piston chamber under the influence of said
fluid pressure means, each said biassing piston and piston chamber
including respective first and second pairs of stop means which abut each
other to limit respected laterally inward and laterally outward movement
of said biassing pistons depending upon the fluid pressure effect in the
associated piston chamber, and all of said first pairs of stop means
define the operative position of the annular die with an axis thereof
coaxial to that of said punch axis whereby lateral outward movement by
said annular die to release any one of said first pair of stop means
automatically establishes a fluid pressure restoration force in the
associated piston chamber absent correspondingly effecting the remaining
biassing pistons.
Description
This invention relates to the production of metal containers and, in
particular, to the production of thin-walled metal cans by the so-called
"drawing and wall-ironing" (DWI) process.
In a DWI process, a flat circular blank is drawn through one or more
drawing dies to form a shallow cup. Thereafter, the cup, which is mounted
on the free end of a close-fitting punch or ram, is subjected to a second,
"wall-ironing" stage by being pushed through one or more annular
wall-ironing dies for the purpose of effecting an elongation of the wall
of the cup.
Such elongation is produced by virtue of a very high radial compression
which is generated in the wall of the cup as the cup is pushed
progressively through the throat of the annular die or dies.
The most common form of tool used in this process is rigid. In this type of
tool, the ironing die-rings together with associated rings, for example
drawing and guiding rings, are rigidly mounted as an assembly on a machine
bed. A horizontally disposed, cantilever-mounted, punch is arranged for
movement in a horizontal direction along the machine bed towards and away
from the die ring assembly.
It has been found that satisfactory operation of the DWI process can be
upset or prevented by deflections of the cantilevered punch caused by such
factors as uneven distribution of temperature around the punch surface and
innacurate centering of cups on the punch. Because of these factors it can
happen that the punch deflects from its desired true alignment with the
longitudinal axis of the die assembly.
In order to accommodate such deflection of the punch from its desired
central position, it has been proposed to mount a wall-ironing die
resiliently, for example upon rubber O-rings, so that the die is able to
undergo limited movement laterally, that is to say transversely of the
punch axis, from a central position.
In U.S. Pat. No. 4,173,882 (Reynolds Metal Company) it is proposed that the
wall-ironing die should be engaged by a series of spring fingers which
engage the die around its circumference and which, due to their
spring-like nature, realign the die to its normally centered position when
the off-centre forces exerted on the die by the punch are removed. It will
be understood that in order to achieve this effect the resultant of the
biassing forces produced by the spring fingers when in its required
central position on the punch axis must be substantially zero.
A disadvantage of the previously proposed methods of mounting a
wall-ironing die for resilient lateral movement has been the relatively
limited restoring force which has been available. For example, in the
proposed arrangement of U.S. Pat. No. 4,173,882 the restoring force
provided by the spring fingers will progressively increase in a
substantially linear manner, ie at the spring rate, in proportion to the
distance through which the die moves from its central position. The
restoring forces generated when the die undergoes small lateral movement
from its central position are correspondingly small, and likewise the
acceleration which is imparted to the die for its return movement when the
off-centre forces on the die have ceased is correspondingly limited. This
limited restoring force may therefore present an upper limit to can
production at very high production rates, for example greater than 300
cans per minute.
A further shortcoming of the arrangement disclosed in U.S. Pat. No.
4,173,852 is that if each spring finger is arranged to engage the die with
preloading (so that it exerts a positive force on the die even when the
die is in its central position), any spring finger which is disposed on
the upstream side of a lateral die movement, that is to say, on the side
of the die opposite to its direction of movement, will act against the one
or more spring fingers in the downstream direction of movement which are
seeking to restore the die to its central position. Again, therefore, the
resultant restoring force exerted on the die is subject to undesired
limitation.
The invention seeks to remove or substantially reduce the shortcomings
noted above.
According to the present invention from a first aspect there is provided an
apparatus for the production of a metal container, which comprises:
at least one die, and a punch movable through the die along an axis, the
die being movable laterally in relation to the axis from a predetermined
central position, and
biassing means comprising a plurality of biassing elements spaced around
the die at predetermined locations and each arranged for biassing the die
towards the said predetermined central position when the die is laterally
displaced from that position and towards the biassing element;
wherein each biassing element is ineffective upon the die when the die is
laterally displaced from its central position and away from the biassing
element.
According to the present invention from a second aspect there is provided
an apparatus for the production of a metal container, which comprises:
at least one die, and a punch movable through the die along an axis, the
die being movable laterally in relation to the axis from a predetermined
central position;
biassing means for the die, the biassing means comprising
a) a plurality of biassing elements spaced around the die and each subject
to a force biassing the die towards its central position when the die is
laterally displaced from that position and towards the biassing element,
and
b) fluid pressure means continuously effective to exert the said force on
each said biassing element; and
disabling means for the biassing means, the disabling means being arranged
for rendering each biassing element ineffective upon the die when the die
is laterally displaced from its central position and away from the
biassing element, despite the said force continuously exerted on the
biassing element by the fluid pressure means. Because of the presence of
the disabling means, substantially no force opposes return of the die to
its centered position (except the usual inertial forces), despite the
continuous operation and availability of the biassing elements.
The biassing means is preferably operated by fluid pressure, especially
pneumatic pressure, and the disabling means preferably comprises stop
means providing a mechanical stop by which the disablement of each
biassing element on the upstream side of lateral die displacement is
effected.
In one described embodiment, the biassing elements are spaced and radially
moveable pistons which are individually urged towards the punch by
compressed air which may be fed from a common gallery. The die or dies are
moveable laterally through a small distance to accommodate punch
misalignment. Restoring force to return each die to its central position
is generated pneumatically by the pistons which are individually subject
to stop means by which they are made ineffective for generating force on
the die when the die moves from its central position in the direction away
from the piston. A very high restoring force can therefore be generated
for small off-centre movements of the die. In this arrangement the stop
means comprises an annulus disposed to limit the travel of the pistons in
the inward direction.
In an alternative described embodiment, the biassing means comprises a
plurality of segment pistons which are urged radially outwards against
parts of a fixed structure by pneumatic means in the form of an air bag
which is interposed between the die and the pistons.
The air bag accommodates lateral movement of the die and generates
restoring force by engagement made with the fixed structure by any piston
which is on the downstream side of the die movement, that is to say, in
the direction of which the die is moving. A piston which is on the
upstream side of the die movement, however, is lifted away from engagement
with the fixed structure, so that in that region the biassing means
generates no resultant inward force upon the die. Any restoring force
generated by the one or more downstream pistons of the biassing means is
therefore not counteracted.
In both embodiments, in the central position of the or each die no
resultant lateral force is applied to the die by the biassing means.
However, any lateral movement of the die from that position results in one
or more of the biassing elements applying a restoring force, whilst the
other biassing elements are rendered inactive. Hence, the smallest lateral
movement causes a significant restoring force to be applied.
Preferably, as particularly described, first and second dies are coupled
together for lateral movement in pairs, there being typically one guide
ring for each die pair and one ironing ring. Coupling is achieved in the
first embodiment by a forked component passing through a spacer between
the dies. In the second embodiment the dies of a die pair are again
separated by a spacer and they are coupled together by interlocking
fingers extending from parts of a housing member by which the pistons and
the air bag for each die are located.
In each embodiment very high pressure lubricant/coolant fluid is fed
through the spacer between the first and second coupled dies,
advantageously at a pressure of at least 500 psi, most preferably 2000
psi. The high pressure fluid forces the metal of the can onto the punch,
clamping the workpiece firmly onto the punch as it enters the ironing
ring. The use of such high pressures may also act to centre the punch.
Careful control of the punch travel by means of the pistons and the fluid
may enable an increased wall reduction of the can wall thickness to be
achieved, thereby reducing the number of ironing operations required to
form the finished can. The provision of the high pressure fluid has little
or no effect on the centering of the dies by the biassing means as
described above.
As in the first described embodiment the apparatus may have a second die
pair of third and fourth dies, again typically a guide ring/ironing ring
pair. In such an arrangement the apparatus may include a supply of low
pressure lubricant between the two pairs of dies, ie between the second
and third dies. The second and fourth dies may be sizing dies which act as
guide rings.
Preferred embodiments of the invention will now be described, by way of
example only, with reference to the drawings, in which:
FIG. 1 is a sectional view taken on the punch axis of a die set according
to a first embodiment of the invention and comprising two die pairs.
FIG. 2 is a cross-sectional view through one die pair, takenon line A--A of
FIG. 1;
FIG. 3 is a side view of the forked connector forming part of each die
pair;
FIG. 4 is a cross-sectional view taken on line B--B of FIG. 1;
FIG. 5 is a partially scrap-sectioned view of a die pair of a second
embodiment; and
FIG. 6 is a sectioned side view of the die pair of FIG. 5.
FIG. 1 is a side view of a die set 8, through which a punch passes in the
direction of the arrow X in order to wall iron a can body cup carried on
the punch. The die set of FIG. 1 comprises two pairs of dies 1, 2, 3 and
4, the two pairs being separated by a fixed spacer 5 in relation to which
the dies are laterally movable. Each of the dies has a carbide insert 6 to
provide wear resistance. Dies 1 and 3 are ironing dies, whereas dies 2 and
4 are sizing dies/guide rings. Dies 1 and 2, and dies 3 and 4 are fixed in
their pairs by means of a respective forked connector 7.
For each die pair a fixed housing member 10 provides a spacer between the
dies and has a central channel 11 through which high pressure coolant at
typically 2000 psi is supplied to the cup exterior in order to lubricate
the passage of the cup through the dies.
The spacer 5 between the pairs of dies also has a central channel 12
through which coolant is supplied, in this case at low pressure, typically
30 psi. Around the circumference of the spacer 5, two sets of cylindrical
pistons 15 are provided, one set for each die pair. Each piston is located
and movable within a respective radially directed chamber 16. Fixed to
each side of the spacer 5 are annular piston stops 17 arranged to limit
radially inward movement of the pistons 15 of the die pair on that side.
Outward movement of the pistons is limited by shoulders or first step
means 19 contacting second stop means "unnumbered" defined by the faces
"unnumbered" of the piston 15.
For each set of pistons the piston chambers 16 are fed by a common
peripheral gallery 18 from which a compressed air feed passes to the
chambers 16 so as to urge the pistons 15 radially inwardly against the
respective stop 17. By avoiding the need for parts which are required to
flex this pneumatic biassing of the pistons eliminates or substantially
limits material fatigue to a minimum.
In use, as the cantilevered punch passes through the dies, deflection of
the punch from its central axial position can cause the pairs of dies to
move laterally (and independantly) from their own central positions. For
each die pair the available lateral movement is determined by the size of
a gap 13 which is provided between the external surface of the forked
connector 7 and an internal shoulder 14 of the housing 10.
In the central position of each die pair the associated pistons 15 abut not
only the piston stop 17 as mentioned above but also the exterior of a die
2 or 3 of the die pair. Therefore, any lateral movement of the die pair in
the direction of a piston will push the piston backwardly against the
pressure of air behind it, and will lift the piston off the respective
piston stop. The piston is accordingly able to exert a restoring force
biassing the die pair towards its central position. This restoring force
is available as soon as the piston leaves the piston stop, and its
magnitude is determined by the effective area of the piston and the
pressure of the air supply. It may therefore be substantially constant
(and of large magnitude) over the whole travel which the piston is
required to undergo until the die pair has been restored to its central
position. The piston then mechanically re-engages the stop 17 and is
rendered no longer effective upon the die pair.
It will thus be understood that downstream of the lateral movement of each
die pair the respective pistons 15 are lifted off their stop 17 and are
then effective to generate substantially constant forces in the sense to
return the die pair to its central position. Any piston, however, which is
located in the upstream direction of the pair movement remains engaged
with the piston stop, and so can not exert any force upon the die pair.
Thus the restoring forces generated on the downstream side of the die pair
are not counteracted to any degree by opposing forces generated on the
upstream side of the die pair. It will accordingly be seen that the stop
provides a stop means by which the upstream pistons 15 are disabled from
exerting or, in other words, are rendered ineffective to exert, a biassing
force upon the die pair, even though they continue to generate inward
force whilst the die pair is laterally displaced.
FIG. 2 is a cross-section viewed in the direction of A--A of FIG. 1. In
this figure, channel 11 through the housing 10 of die pair 1, 2 can be
seen together with further smaller branch channels from the main channel
which direct a vortex of coolant/lubricant onto the cup-punch passing
through the dies. Prongs 8 of the forked connector 7 extend from an
annulus 9 which forms the body of the connector and which surrounds the
die 1. A cross-section of the forked connector is shown in FIG. 3.
FIG. 4 is a cross-sectional view along the line B--B of FIG. 1 which passes
through the pistons and looks towards the spacer 5 in the direction of
punch travel. From that figure it will be understood how the compressed
air is fed to the piston chambers 16 of each set by the common gallery 18.
It will also be seen that 24 pistons 15 are provided, spaced regularly
around the die/spacer. Within the pistons, the piston stop 17 and channels
12 for delivery of low pressure lubricant are visible.
In an alternative embodiment, illustrated in figures 5 and 6, the die rings
1, 2 of a die pair are located in an annular housing having inner and
outer members 20, 21. The inner housing member 20 is itself in two parts,
one for each die ring. Each part is secured to its repective die ring, and
moveable with it laterally of the central axis. Trapped inside each part
of the inner housing member 20 are three peripherally spaced segment
pistons 22, and an air bag 25 interposed between the segment pistons and
the respective die ring. Under the action of pneumatic pressure in the air
bag, the pistons are urged radially outwards, and project through gaps in
the housing to free ends 50. This travel is limited by engagement of
flanges 23 on the segment pistons with complementary formations (not
referenced) on the inside of the inner housing member 20.
As shown in FIG. 6, when the die pair is located in its aligned central
position the segment pistons engage the inner housing member 20 with their
flanges 23 and at the same time their free outer ends 50 engage wear bars
or fixed abutment means 26, 27 and 28 forming part of the fixed structure
of the apparatus. Therefore, when the die pair is deflected away from its
central position, the pistons on the downstream side of the movement are
pushed inwardly against the air bag and their respective flanges 23 are
forced out of contact with the inner housing member. For those pistons,
therefore, the compressed air bag generates a restoring force opposing
further movement of the die pair away from its central position. The
piston or pistons on the upstream side of the die pair movement, however,
lose contact with their wear bars whilst maintaining contact at their
flanges 23. They are therefore rendered incapable of transmitting inward
biassing force to the die and so of counteracting any restoring force
generated by the downstream pistons. As with the first embodiment, each
piston 22 is able to generate maximum restoring force as soon as it is
free to do so.
It will be seen that in this second embodiment the parts of the inner
housing member 20 provide stop means by which the upstream segment pistons
22 are rendered ineffective to transmit biassing force to the dies, even
though those segment pistons are being continuously acted upon by the air
bags 25 whilst the dies are laterally displaced.
As in the first embodiment, the rings of the second embodiment are arranged
in pairs comprising one ironing ring 30 and one guide ring 32. In this
second embodiment, however, the rings are linked together by means of a
push fit between fingers 31, 33 extending from the parts of the inner
housing 20 member. The parts of the inner housing member are further
secured together by means of spring pins 34 (FIG. 5).
The outer housing member 21 is generally T-shaped in cross-section and
arranged to act as a spacer between the rings 30, 32. It is formed with
passages for high pressure lubricant/coolant in a similar arrangement to
the passages in the spacers between the dies of each die pair of the first
embodiment.
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